Sorption cooling systems and climate control using multi-channel thermal swing adsorption

ABSTRACT

Sorption cooling systems and methods for using sorption cooling systems, particularly to control the interior climate of vehicles, buildings, appliances and other enclosed spaces. The sorption cooling systems may incorporate sorbent beds having a low thermal mass that are capable of rapid cycle times to increase the efficiency of the sorption cooling systems.

RELATED APPLICATIONS

This application claims priority as a non-provisional application of U.S. Provisional Patent Application No. 61/524,219, filed Aug. 16, 2011, entitled “SORPTION COOLING SYSTEMS AND CLIMATE CONTROL USING MULTI-CHANNEL THERMAL SWING ADSORPTION”, the entirety of which is hereby incorporated by reference.

FIELD

The present invention relates to the field of sorption cooling systems and the use of sorption cooling systems to control the interior climate of vehicles, buildings, appliances and other enclosed spaces. In particular, the present invention relates to sorbent beds having a low thermal mass and capable of rapid cycle times to increase the efficiency of a sorption cooling system.

BACKGROUND

Sorption cooling systems provide cooling by evaporation of a refrigerant (e.g., water), followed by sorption (e.g., adsorption or absorption) of the refrigerant onto a sorbent material. The refrigerant must then be desorbed from the sorbent, such as by heating the sorbent. Using waste heat (e.g., from a vehicle engine or a cogeneration facility) for regeneration of the sorbent is potentially very attractive from an energy efficiency and emissions viewpoint. By way of example, an order of magnitude reduction in energy consumption for air conditioning units (e.g., stationary or mobile air conditioning units) could be achieved by eliminating or reducing the use of the energy-intensive compressor and using that energy (or some fraction thereof) for pumps and blowers in a sorption cooling system. This potentially translates into an effective “COP” (coefficient of performance) of 15 to 25 as compared to a COP of 2 that is typical for most vapor compression air conditioning or refrigeration systems. Other potential advantages include: 1) lower system weight; 2) reduced emissions; 3) in vehicle applications, cooling and/or heating before engine start-up; and 4) the use of an environmentally friendly refrigerant (water vapor).

One example of a sorption cooling system of the general type described herein is disclosed in U.S. Pat. No. 7,143,589 by Smith et al., which is incorporated herein by reference in its entirety.

In addition to their use in sorption cooling systems, sorbent beds may also be used as a component in a drying system to reduce the water vapor in the atmosphere and thereby reduce the water vapor condensation load that is associated with traditional cooling devices such as compressor-based air conditioners.

SUMMARY

Despite the significant advances disclosed by Smith et al. in U.S. Pat. No. 7,143,589, there remains a need for high efficiency sorption cooling systems that can replace and/or supplement traditional compressor-based cooling systems in climate control applications such as in vehicles and buildings, and in cooling of refrigeration devices (e.g., in stationary appliances such as refrigerators and freezers as well as mobile applications such as reefer trucks, cargo ships and airplanes).

Sorption cooling systems include at least an evaporator (where the refrigerant liquid evaporates to provide cooling) and a sorbent to sorb (e.g., adsorb and/or absorb) the evaporated refrigerant. The sorbent (e.g., in a sorbent bed structure) is cycled between the sorption phase, the regeneration phase (where the sorbent material is regenerated by desorbing the refrigerant) and a cooling phase (where the sorbent is cooled before the next sorption phase). Since the cooling rate is fixed by the water evaporation rate, the total size required for each sorbent bed depends upon how much refrigerant (e.g., water) it must sorb. Long cycle times lead to large beds but low parasitic energy loss (i.e., energy used to heat and cool beds beyond the latent heat of water vaporization during regeneration). Conversely, very short cycle times may lead to very small beds (relative to current vapor compression systems) but relatively high parasitic losses and small beds may ultimately be limited by available heat and mass transfer rates. Parasitic losses may advantageously be somewhat reduced by low thermal mass beds (e.g., high desiccant capacity, plastic structures). If the cycle time is on the order of tens of minutes, the required bed sizes will be very large.

Therefore, in one embodiment, an improved sorption cooling device is provided. The sorption cooling device includes a sorbent bed having a very low thermal mass, enabling extremely short cycle times (i.e., the time to desorb the refrigerant and cool the sorbent before the next sorption phase). In one aspect, the sorbent bed can advantageously provide cooling of at least 1 kW per 350 grams of sorbent (e.g., desiccant), such as at least 1 kW of cooling per 200 grams of sorbent, and even at least 1 kW of cooling per 150 grams of sorbent. In one aspect, for an 8 kW sorption cooling system (e.g., sufficient cooling for a typical automotive air conditioning application) the sorption cooling device may include not greater than about 500 grams of sorbent.

Advantageously, low-grade waste heat (e.g., from the internal combustion engine of a vehicle or from a cogeneration plant) can provide the necessary thermal energy to regenerate the sorbent bed of the sorption cooling system by desorbing the refrigerant. The sorbent bed may utilize a high capacity desiccant that can be regenerated at a relatively low temperature, preferably avoiding the use of vehicle exhaust gas for desorption in vehicle applications.

The sorption cooling devices may include an evaporator, a refrigerant source such as a condenser that is adapted to fluidly communicate with the evaporator, and one or more sorbent beds adapted to fluidly communicate with the condenser and the evaporator. In one aspect, the refrigerant fluid of the sorption cooling system comprises water.

The plurality of sorbent beds may include a fluid impermeable casing having a refrigerant inlet, a refrigerant outlet, a coolant inlet and coolant outlet. The sorbent beds may also include a plurality of sorbent sheets (e.g., desiccant sheets), such as first and second sorbent sheets. The sorbent sheets may generally have a sorbent first side and are covered by a fluid impermeable barrier on a second (opposite) side. The sorbent sheets each include at least one aperture, such as at least two apertures, extending through the sorbent sheets. The apertures of the sorbent sheets may be a portion of one of a refrigerant flow path and a coolant flow path. In a particular embodiment, at least one of the refrigerant flow path and the coolant flow path is non-linear. In one embodiment, both the refrigerant flow path and the coolant flow path are non-linear.

A refrigerant flow path for flowing a refrigerant fluid between the refrigerant inlet and the refrigerant outlet extends through each sorbent bed. The refrigerant flow path is at least partially defined by the first (sorbent) sides of the sorbent sheets, which define a refrigerant flow path having a refrigerant flow channel length and a gap height. Preferably, the sorbent sides of opposing sorbent sheets face each other to help define at least a portion of the refrigerant flow path.

A coolant liquid flow path for flowing a coolant liquid between the coolant inlet and coolant outlet also extends through each sorbent bed. The coolant liquid flow path defines a coolant fluid flow channel length and gap height. The coolant flow path is fluidly isolated from the refrigerant flow path, but is adjacent to at least one of the sorbent sheets. In one embodiment, the apertures are a portion of the coolant flow path and the coolant flow path is non-linear.

The sorbent beds may include one or more of the following features:

1) Channel length and height: For refrigerant (air) flow, channel lengths may be on the order of 1″ (25 mm) in length and gap heights may be 0.5 to 1 mm. For the liquid refrigerant side, the channel length may be on the order of 12″ (300 mm) and the gap may be varied between 0.5 mm and 2 mm.

2) Pressure and pressure drop: Typical pressure drops on the liquid coolant side are typically 1-2 psia, whereas the refrigerant pressure drop may be between 0.5 and 2 inches of H₂O.

3) Thermal mass: Critical to the ability to rapidly cycle through sorption, desorption and cooling cycles is reducing the thermal mass of the system. A number of steps may be undertaken to reduce thermal mass. These may include:

1) Use of 3-way valves to reduce the amount of refrigerant that must be swept out during a cycle change;

2) Reduced manifold volume in the stack to reduce the amount of refrigerant that must be swept out during cycling;

3) Reduced refrigerant channel height to reduce the amount of refrigerant that must be swept out during a cycle change and increase the heat transfer coefficient;

4) Elimination of water channel spacers to reduce plastic mass that is in direct contact with refrigerant—water pressure may be used to create a gap; and/or

5) Sorbent sheets which are both thinner (e.g., 0.15 mm) and which have a higher sorbent loading (e.g., greater than 50% and up to 70%). For example, the sorbent sheets may comprise a porous fluoropolymer (e.g., PTFE).

These aspects of the invention, alone or in combination, may lead to dramatic improvements in performance of the sorption cooling device. This may be evident from the reduction in the three different sorbent devices (stacks) illustrated in FIG. 1. Each of these sorbent devices has a nominal rating of 1 kW of cooling and the size reduction is related to performance improvements primarily due to lower thermal mass.

The thermal mass reduction also advantageously enables rapid cycling such that sorption in one sorbent bed may occur for the same length of time as both the desorption and cooling cycles combined in another bed. This enables operation using only two sorbent beds instead of three beds, since desorption and cooling can occur in the same bed. In addition to the mass reduction of the device from eliminating one bed, the issues of air and water flow switching are greatly simplified.

Key performance parameters of the sorbent bed may include:

-   -   1) Heat up and cool down times may be less than 10 seconds;     -   2) The sorbent bed may enable 1 kW of cooling for not greater         than 75 grams of desiccant; and/or     -   4) Despite only running a conservative desorption temperature of         80° C., desorption vapor pressures over 100 mbar may be         achieved, which will help reduce the condenser size

The possibility of 2 bed operation at 75 grams/kW (1 bed) or 150 grams/kW (system) may be achieved. With higher vapor flow rates, this can be reduced to ˜100 grams/kW (system). With a thinner sorbent sheet, 60 grams/kW (system) may be achievable. In other words, for an 8 kW air conditioning system, only about one pound of sorbent (e.g., desiccant) may be necessary.

The present invention also may include the use of a (e.g., single) sorption bed as a dryer for air streams containing water vapor. This could be either as a dryer for air entering a conventional vapor-compression air conditioning system, for entering the evaporator of the waste heat powered system disclosed herein, or simply for dehumidification of building or other interior climate. In air conditioning, a significant portion of the thermal load arises from condensing water vapor. Because of the rapid desorption and cooling cycles, the possibility of sorbing water for much longer periods of time followed by desorption and cooling was also studied, and duty cycles (i.e. the fraction of time that a bed is adsorbing) of ˜80% may be achieved. This means that a dryer using this technology could be sorbing 80% of the time and desorbing to the outside atmosphere during the remaining 20% of the time. Since it is a single bed structure, air and water valving may be much simpler. This has applications in many areas where waste heat is available and water vapor removal/control is advantageous.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates three sorbent devices (e.g., stacks) having a nominal rating of 1 kw of cooling.

FIG. 2 illustrates a cross-sectional view of a sorption cooling device.

FIG. 3 schematically illustrates a sorption cooling system.

FIG. 4 schematically illustrates a sorption cooling system.

FIG. 5 schematically illustrates a sorption cooling system, including a cooling fluid source.

FIG. 6 is a flow diagram depicting one embodiment of a dehumidification system

FIG. 7 illustrates a cross-sectional, perspective view of one embodiment of an absorbent bed.

FIG. 8 illustrates a cross-sectional, perspective view of one embodiment of an adsorbent bed.

FIG. 9A illustrates a cross-sectional, perspective view of one embodiment of an adsorbent bed.

FIG. 9B illustrates a top view of one embodiment of a portion of a fluid casing of an adsorbent bed.

FIG. 9C illustrates a top view of one embodiment of a desiccant sheet of an adsorbent bed.

FIG. 9D illustrates a top view of one embodiment of a spacing material of an adsorbent bed.

FIG. 9E illustrates a top view of one embodiment of a portion of a fluid casing of an adsorbent bed.

FIG. 10 illustrates a cross-sectional, perspective view of one embodiment of an adsorbent bed.

FIG. 11A illustrates a side view of one embodiment of an adsorbent bed.

FIG. 11B illustrates a side view of one embodiment of an adsorbent bed.

FIG. 12 illustrates a cross-sectional view of one embodiment of an adsorbent bed.

FIG. 12A is a graph depicting water adsorption isotherms for CaCl₂ and LiCl ______.

FIG. 13 schematically illustrates a desiccant stack test stand for a 1 KW desiccant cooler.

FIG. 14 illustrates the thermal response of an adsorbent stack for 35° C. cold and 80° C. water with and without ambient air flow.

FIG. 15 schematically illustrates a cross-sectional view of an adsorbent stack structure.

FIG. 16 illustrates the thermal response of an adsorbent stack.

FIG. 17 illustrates the thermal response of an adsorbent stack.

FIG. 18 illustrates the thermal response of an adsorbent stack.

FIG. 19 illustrates the thermal response of an adsorbent stack.

FIG. 20 illustrates the thermal response of an adsorbent stack.

FIG. 21 illustrates the thermal response of an adsorbent stack.

FIG. 22 illustrates the thermal response of an adsorbent stack.

FIG. 23 illustrates the thermal response of an adsorbent stack.

DESCRIPTION

In one embodiment, an improved sorption cooling system is provided that may include an improved, lightweight sorbent bed structure capable of sorbing a relatively high amount of refrigerant such as water. The sorption cooling system may also include an improved lightweight, compact evaporator capable of evaporating refrigerant at rates sufficient to sustain cooling operations. The sorption cooling system may be used to provide cooled fluid, such as cooled air or cooled water, to control the atmosphere in vehicles (e.g., automobiles), to control the atmosphere in buildings and/or to provide refrigeration such as in appliances, reefer trucks, long-distance shipping containers and the like.

The general operation of a sorption cooling system is well known in the art. Referring to FIG. 2, a sorption cooling system 100 includes an evaporator 102, a sorption bed 106 and a refrigerant source 104. Refrigerant supplied to the evaporator 102 from the refrigerant source 104 evaporates in the evaporator 102, thereby cooling a portion of the evaporator 102. The evaporated refrigerant is then sorbed (e.g., adsorbed and/or absorbed) in a sorption bed 106 to remove the vaporous refrigerant from the evaporator 102. A vapor passageway 105 enables the evaporated fluid to flow from the evaporator 102 to the sorption bed 106.

The devices and systems disclosed herein enable the use of sorption techniques to provide cooling using a solid-phase, high-capacity desiccant that is capable of sorbing a significant amount of vapor-phase refrigerant (water) and that is also capable of desorbing most or all sorbed refrigerant at temperatures of not greater than about 120° C. during regeneration operations.

The mechanism by which the sorbent material such as a desiccant functions can be adsorption, absorption or a combination of adsorption and absorption, and as used herein, the terms sorb, sorbed, sorptive, sorption and the like refer to the retention of fluid, regardless of the actual mechanism by which the fluid is retained. Likewise, the mechanism by which the sorbed refrigerant is released from the high-capacity desiccant can be desorption, desorbtion, or a combination of desorption and desorbtion, and as used herein, the terms desorb, desorbtive, desorbtion and the like, as well as the terms regenerate, regenerable, regenerated and the like when used in reference to the sorption material, refer to the release of fluid from the sorbent, regardless of the actual mechanism by which the fluid is released.

Sorption cooling systems can generally be categorized into two types: in-situ regenerable and ex-situ regenerable. In-situ regenerable sorption cooling systems are generally capable of regenerating the sorbed refrigerant from the sorbent bed during operation of the sorption cooling system, and therefore generally include a means for regenerating the sorbed refrigerant and subsequently liquefying such refrigerant. Generally these means include a heat source for heating the sorbent bed and a cooling source for cooling the regenerated refrigerant into a liquid. Often, the cooling source is a condenser.

Ex-situ regenerable sorption cooling systems are generally not capable of regenerating the sorbed refrigerant from the sorbent bed during operation of the sorption cooling system. Therefore, ex-situ regenerable sorption cooling systems are not generally used in most cooling applications.

According to one aspect, the sorption cooling system is an in-situ sorption cooling system utilized in providing cooled air for climate control. One embodiment of such a sorption cooling system is depicted in FIGS. 3-4. According to this embodiment, the sorption cooling system 400 includes an evaporator 402, a condenser 404 in fluid communication with the evaporator 402, a plurality of sorbent beds 406, 408 adapted to fluidly communicate with the evaporator 402 and condenser 404, and a hot fluid source 416 for providing hot fluid to the sorbent beds. During operation, liquid refrigerant flows from the condenser 404, via evaporator supply line 410, to the evaporator 402, where the refrigerant is evaporated. As is known in the art, this evaporation cools the evaporator 402. The evaporator 402 is situated such that at least one surface is in thermal communication with a (flowing) air stream 420 to cool the air stream.

The sorbent beds 406, 408 may work in parallel and in two operating phases to enable continuous cooling operations. In the first phase of operation, as depicted in FIG. 3, a first adsorbent bed 406 is heated by circulating hot fluid through the first sorbent bed 406 via a hot fluid flow path. The hot fluid is circulated through the first sorbent bed 406, and is supplied from hot fluid source 416 via hot fluid supply line 412. Hot fluid is returned to the hot fluid source via hot fluid return line 414. The heated first sorbent bed 406 desorbs its sorbed refrigerant, which is then supplied to the condenser 404 via condenser supply line 422 where it is liquefied. The liquid refrigerant can then be provided to the evaporator 402 via evaporator supply line 410 to sustain cooling operations. Also during the first phase of operation, the second sorbent bed 408 supplies “dry air” to the evaporator 402 via air supply line 424, such as by a fan (not depicted). The dry air stream helps evaporate refrigerant, and exits the evaporator 402 as a “wet air” stream, where it is returned to the second sorbent bed 408 via air return line 426. The returned wet air stream flows through the second sorbent bed 408 via a refrigerant flow path, where refrigerant contained in the wet air stream is sorbed within the second sorbent bed 408, such as by a desiccant. Pipes, tubing, valves and the like may be used to control the flow of fluid in the system.

As used herein, the term “dry air” refers to an air or other gaseous stream containing a relatively small amount or no refrigerant. As used herein, the term “wet air” refers to an air or other gaseous stream containing a relatively high or even saturated amount of refrigerant. As noted below, a variety of refrigerants can be used within the sorption cooling system of the present invention, including water. However, neither the term “dry air” nor the term “wet air” is meant to imply the absence or presence of water within such air unless the refrigerant comprises water.

The first phase of operation may continue until the efficiency of sorption by the second sorbent bed 408 reaches a threshold level of sorption and/or the first sorbent bed 406 is sufficiently regenerated (i.e., a predetermined amount of refrigerant is removed from the first sorbent bed), after which the first phase of operation is ceased and the second phase of operation begins, such as by switching valves and/or other mechanisms within the system. In the second phase of operation, the roles of the first and second sorbent beds 406, 408 are switched, where the first sorbent bed 406 supplies dry air to the evaporator and the second sorbent bed 408 is regenerated and supplies refrigerant to the condenser 404, as depicted in FIG. 4. This enables continuous operation of the sorption cooling system 400.

Generally, the sorbent beds are structured to contain distinct (e.g., separate) refrigerant and hot fluid flow paths. Generally, the refrigerant and hot fluid flow paths are fluidly isolated. The refrigerant flow path generally allows a fluid (e.g., a gas) to flow through the sorbent bed and contact the desiccant material. The hot fluid flow path is fluidly isolated from the sorbent material of the sorbent beds and refrigerant flow path, but is adjacent to such sorbent material for providing thermal communication thereto, as discussed in further detail below.

For convenience, the term “desiccant”, “desiccant material” and the like are used herein to describe the sorbent material utilized in the sorbent beds, but such terms are not intended to limit the adsorbent material to just desiccants. The sorbent can be any material capable of sorbing vaporous refrigerant and that is also capable of regenerating (i.e., desorbing) refrigerant at temperatures not greater than 120° C. or less.

The sorption cooling system may be a closed-loop system. The sorption cooling system may be contained in a hermetically sealed system to maintain refrigerant to sorbent ratios and to effect the desired cooling, as well as to prevent contamination of the sorbent. For example, if a high-capacity desiccant is used in the sorbent bed, it cannot be exposed to atmospheric conditions where water vapor and contaminants are present. Exposure to the atmosphere will likely poison and/or sterilize the desiccant.

As noted above, hot fluid can be supplied to the sorbent beds to regenerate the refrigerant contained therein. In one embodiment, the hot fluid is a liquid-phase fluid. In one embodiment, the hot fluid is a liquid-phase fluid used in the cooling operations of an internal combustion engine, such as radiator coolant fluid (e.g., ethylene glycol), and the coolant source is the radiator or similar structure of a vehicle. In another embodiment, the hot fluid is heated using waste heat from a cogeneration facility. Using waste heat enables the regeneration of the sorbent bed without supplying a secondary heat source, and provides efficiency in operating the sorption cooling system. Moreover, the use of a hot liquid-phase fluid, as opposed to gas-phase fluid, is more efficient in regenerating the sorbent bed, as the hot liquid-phase fluid will, in general, more quickly transfer its heat to the bed.

According to another aspect, the sorption cooling system includes a cooling fluid source for use in cooling the sorbent beds. One embodiment utilizing such a cooling fluid source is depicted in FIG. 5. According to this embodiment, the cooling fluid source 418 may be plumbed to the sorbent beds 406, 408, 409 to provide a cold fluid (as opposed to the hot fluid of the first fluid source) to help cool the sorbent beds 406, 408, 409 during a cool-off phase and/or help increase the sorption capacity of the sorbent during sorption activity.

As noted above, the sorbent beds are generally regenerated by heating the sorbent material contained therein. After regeneration, the sorbent material should generally be allowed to return to a certain (lower) temperature before beginning sorption activities. A significant amount of time can elapse between regeneration activities and the time at which the sorbent has returned to the certain temperature. This time lapse can affect the efficiency of operation of the sorption cooling system. Thus, it may be desirable to provide a third operating phase where a cold fluid is supplied to a sorbent bed after its regeneration operation to more quickly reduce its temperature to an acceptable level. Therefore, according to one embodiment, a second fluid source 418 may be provided, which can provide a cold (relatively) coolant to a sorbent bed during its third operating phase (cool-off). As depicted in FIG. 5, a first sorbent bed 406 is operating in a regeneration phase, and is being heated by a hot fluid from a first fluid source 416, as described above. A second sorbent bed 408 is operating in an adsorption phase, as described above. A cold fluid circulates through a third sorbent bed 409 via coolant supply and return lines 428, 430 to cool the third sorbent bed 409.

The cold fluid may also be supplied to a sorbent bed conducting sorption operations. Generally, the sorption capacity of the desiccant is a function of its temperature; at lower temperatures the desiccant is capable of sorbing more refrigerant. As depicted in FIG. 5, the cold fluid can circulate through the second sorbent bed 408 via coolant supply and return lines 432, 434, to increase the sorption capacity of the second sorbent bed 408 and, therefore, the efficiency of the sorption cooling system.

As used herein, the terms “hot fluid” and “cold fluid” refers to the temperature of the fluid in relation to the temperature of the sorbent beds, and more specifically to the temperature of desiccant sheets within such beds. Thus, a hot fluid is generally at a temperature greater than that of the desiccant materials and a cold fluid is at a temperature less than that of the desiccant materials.

The cold fluid may be any fluid adapted to flow through the fluid flow paths of the sorbent bed. In one embodiment, the cold fluid is a gas, such as ambient air. According to another embodiment the cold fluid is a liquid coolant. In one embodiment for cooling a vehicle, the second cooling fluid source includes a second radiator (in addition to the one normally employed by the vehicle for engine block cooling), which comprises the liquid cold fluid. The size of the second fluid source depends on the quantity of heat that must be removed, which depends upon the sorbent bed's thermal mass. As will be appreciated, since a high-capacity desiccant is generally employed according to the present invention, the sorbent bed's thermal mass will be greatly reduced, and a relatively small second fluid source can be employed to achieve to achieve the necessary cooling rates. In another embodiment, the second cooling fluid source is the condenser and the cold coolant is refrigerant contained within the condenser. Also, while FIG. 5 depicts separate supply and return lines for the hot and cold fluid paths, the cold fluid generally uses the same piping used by the hot fluid and a series of valves and tees are used to affect the appropriate flows.

In another embodiment, the sorption cooling system is operated in conjunction with a conventional (i.e., compression-based) air-conditioning to supplement cooling requirements, such as in a vehicle or building. In one embodiment, a relatively smaller-sized air-conditioner is provided in a vehicle for normal use. When high temperatures and/or high humidity are encountered, a sorption cooling system of the present invention can be used to provide the necessary additional cooling capacity to achieve cooling of the interior of the vehicle. According to this embodiment, sorbent beds employing the high-capacity desiccant may also optionally be used to dehumidify the incoming air to decrease the cooling load.

In another embodiment, two or more sorption cooling systems may be operated in parallel to provide the necessary cooling capacity. Each sorption cooling system is fluidly isolated from the others and can operate independently.

According to yet another embodiment, sorbent beds are used to dry incoming air to reduce the cooling load on the sorption cooling system. As illustrated in FIG. 6, adsorbers 740, 742 are operated in parallel to achieve continuous drying of the incoming air to be cooled by the sorption cooling system. Incoming air 744 flows through a first sorbent bed 740 where it is dried (e.g., via a high capacity desiccant) and exits as dehumidified air 746, which is subsequently flowed proximal to and/or in contact with the evaporator 702. Concurrently, a second sorbent bed 742 is regenerated by heating the bed, such as by using a hot fluid source 716, as described above, and flowing a gas 756 through the second sorbent bed 742 to remove water from the bed 742. Once the first sorbent bed 740 has reached a threshold level of sorption and/or the second sorbent bed 742 has been sufficiently regenerated, the sorbent beds 740, 742 switch dehumidification and regeneration operations. The sorbent beds 740, 742 may optionally also employ the use of a second cold fluid source 718, as described above, to cool such sorbent beds during operation, thereby increasing their sorption capacity. Valve, piping and other materials (not shown) may be used to effect appropriate flows through the sorber beds.

According to another embodiment, an in-situ regenerable sorption cooling system is used to provide a cooled fluid to a building. Waste heat from a cogeneration plant, or other heat source, may be used to provide heat to sorbent beds of a sorption cooling system. Just as was described above with respect to providing cooled air to the cabin of a vehicle, a series of sorbent beds may be operated in parallel to enable the sorption cooling system to provide continuous cooling. However, instead of using a hot coolant from a vehicle, a hot liquid or gas, such as hot water or steam from a cogeneration system, may be circulated through the various sorbent beds to provide the heat necessary to regenerate such beds. The below-described refrigerants, sorbent beds and evaporators may be used according to this embodiment. Also, a multiple-chamber evaporator may be used to provide a cooled fluid to a building.

As noted above, the refrigerant source supplies the evaporator with the necessary refrigerant to provide the cooling. Generally, ex-situ regenerable sorption cooling systems can use any type of refrigerant source, but a simple liquid reservoir, such as a lightweight, flexible plastic housing, will generally suffice so as to minimize the size, weight and complexity of the system. Other types of liquid reservoirs useful in accordance with the present invention are disclosed in commonly-owned U.S. Pat. No. 6,701,724 to Smith et al. and U.S. Pat. No. 6,858,068 to Smith et al., each of which is incorporated herein by reference in its entirety.

In-situ regenerable sorption cooling systems generally are more complex as they require further plumbing to enable fluid communication between the sorbent beds and the refrigerant source and a means to liquefy the vaporous refrigerant. For vehicle cooling applications, an air-cooled condenser is suitable because of its relatively small size and weight, but a water-cooled or an evaporative condenser may also be employed.

Any suitable refrigerant may be employed in the sorption cooling system. In one embodiment, the refrigerant has a high vapor pressure at ambient temperature so that a reduction of pressure will produce a high vapor production rate. Suitable liquids include ammonia, various alcohols such as methyl alcohol or ethyl alcohol, ketones (e.g., acetone) or aldehydes (e.g., acetaldehyde). Other useful liquids can include chlorofluorocarbons (CFC) or hydrochlorofluorocarbons (HCFC) such as FREON (E.I. Dupont de Nemours, Wilmington, Del.), a series of fluorocarbon products such as FREON C318, FREON 114, FREON 21, FREON 11, FREON 114B2, FREON 113 and FREON 112.

In one preferred embodiment, the refrigerant is an aqueous-based liquid and in a particularly preferred embodiment the liquid consists essentially of water. Water is preferred for its very high mass heat of vaporization in addition to its environmental, cost and safety advantages. Approximately 2,500 J of cooling per gram of water evaporated at ambient temperature can be achieved.

The sorbent bed of the sorption cooling system may be any type of sorbent bed adapted to adsorb refrigerant from the evaporator. For example, the sorbent bed may be in the form of a wheel (stationary or rotating) a packed bed, sheet, spiral-wound, or meso-channel parallel plate contactors. In a preferred embodiment, the sorbent bed is lightweight, compact and has a relatively high sorption capacity. The sorbent bed is also preferably capable of quickly sorbing and desorbing refrigerant during sorption and regeneration operations, respectively. One embodiment of such an adsorbent bed is depicted in FIG. 7.

In this embodiment, the sorbent bed 800 includes a fluid impermeable outer casing 801 including a refrigerant inlet 804, a refrigerant outlet 806, fluid inlets 808 and fluid outlets 810. A plurality of desiccant sheets 812 are disposed within the casing, each of the desiccant sheets having at least one aperture 814 extending therethrough. A first side of the desiccant sheets 812 preferably includes a high-capacity desiccant. A second side of the desiccant sheets preferably is covered by a fluid impermeable barrier 816. A refrigerant flow path 818 lies between the refrigerant inlet 804 and refrigerant outlet 806, and a fluid flow path 820 lies between the coolant inlet 808 and coolant outlet 810. Spacing materials 822 may separate the desiccant sheets 812 from one another and help to define the refrigerant and fluid flow paths. The spacing materials 822 and apertures 814 of the desiccant sheets are arranged such that the refrigerant flow path 818 and fluid flow path 820 are fluidly isolated from one another. Generally, the apertures 814 are a portion of and help define either the refrigerant or fluid flow path, although a first set of apertures can be used to define the refrigerant flow path, while a second set of apertures can be used to define the fluid flow path. It will be appreciated that the adsorbent bed can be designed such that the flow paths depicted in FIG. 7 are switched by switching the inlets and outlets with the refrigerant inlets and outlets and flipping the desiccant sheets over, as depicted in FIG. 9.

During sorption operations, vaporous refrigerant from the evaporator flows through the refrigerant flow path 818 contacting the sorbent sections of the desiccant sheets 812, where the refrigerant is adsorbed. As discussed above, during sorbing operations a cold fluid may be circulated through the coolant flow paths 820 to cool the desiccant sheets and increase their sorption capacity. The fluid impermeable barrier 816 on the second side of the desiccant sheets prevents unwanted interaction (e.g., chemical interaction) between the cold fluid and the desiccant.

During regeneration operations, a hot fluid, such as liquid coolant used in the cooling of an internal combustion engine, flows through the fluid flow paths 820 to heat the desiccant, increasing the vapor pressure of the refrigerant sorbed thereon, eventually desorbing at least a portion of, if not all, the refrigerant from the desiccant. The fluid impermeable barrier 816 on the second side of the desiccant sheets 812 prevents unwanted interaction between the hot fluid and the desiccant sheets. Dry air from the condenser or other refrigerant source flows through the refrigerant flow paths 818, to remove the desorbed refrigerant. Wet air exits the sorbent bed 800, and, in the case of in-situ regenerable sorption cooling systems, is returned to the condenser where it is liquefied.

While a single refrigerant and/or fluid flow path may be used in accordance within the present invention, generally the sorbent bed will include a plurality of apertures per desiccant sheet, and a plurality of spacers, fluid inlets and outlets and/or refrigerant inlets and outlets to define a plurality of refrigerant and fluid flow paths. One embodiment of such a sorbent bed is provided in FIGS. 9A-9E. A fluid impermeable casing 1001 includes a plurality of refrigerant inlets 1004, refrigerant outlets 1006, fluid inlets 1008 and fluid outlets 1010. A plurality of desiccant sheets 1012 are disposed within the casing, each of the desiccant sheets having at least one aperture 1014 extending therethrough. A first side of the desiccant sheets preferably includes a high-capacity desiccant. A second side of the desiccant sheets preferably is covered by a fluid impermeable barrier 1016. A plurality of refrigerant flow paths 1018 lie between the refrigerant inlets 1004 and refrigerant outlets 1006, and a plurality of fluid flow paths 1020 lie between the fluid inlets 1008 and fluid outlets 1010. Spacing materials 1022 may separate the desiccant sheets 1012 from one another and help to define the plurality of refrigerant flow paths 1018 and plurality of fluid flow paths 1020. The spacing materials 1022 and apertures 1014 of the desiccant sheets 1012 may be arranged such that the refrigerant flow paths 1018 and coolant flow paths 1020 are fluidly isolated from one another. Generally, the apertures 1014 are a portion of and help define the flow path of either the refrigerant or fluid flow paths, although a first set of apertures can be used to define the refrigerant flow paths and a second set of apertures can be used to define the fluid flow paths. It will be appreciated that the adsorbent bed can be designed such that the flow paths depicted in FIG. 10A are switched by switching the fluid inlets and outlets with the refrigerant inlets and outlets and flipping the desiccant sheets over.

The refrigerant flow paths should generally be designed to maximize mass transfer rates of refrigerant during sorption and regeneration operations. As is discussed in further detail below, mass transfer rates may be maximized by optimizing, inter alia, the surface area of the sorbent sections of the desiccant sheets (i.e., the surface area of the first, sorbent sides of the desiccant sheets minus the area occupied by apertures) and the spacing between the sorbent sides of the desiccant sheets.

The fluid flow paths should generally be designed to maximize heat transfer rates between the desiccant sheets and the fluid. As is discussed in further detail below, fluid cooling or heating rates can be maximized by optimizing, inter alia, the surface area available for heat transfer and the spacing between the fluid impermeable sides of the desiccant sheets.

As noted above, the sorption cooling system may also employ a cooling cycle/phase where the sorbent bed is neither sorbing nor regenerating refrigerant. During cooling operations, a cold coolant may be flowed through the coolant flow path to more quickly cool the desiccant sheets. The fluid impermeable barrier on the second side of the sorbent sheets prevents unwanted chemical interaction between the cold fluid and the desiccant sheets. As will be appreciated, the valves and piping of the sorption cooling system may be arranged and positioned to enable the above cooling operations.

The casing of the sorbent bed is preferably made of a rigid, lightweight and fluid impermeable material to help minimize the mass of the bed, prevent atmospheric interaction with the bed and structurally protect the bed. Non-rigid, fluid-impermeable materials can also be used in some instances. Suitable casing materials include simple plastic films such as polyethylene, nylon, PVC, metal foils with plastic heat seal layers such as sold those by Toyo Aluminum (Japan), metalized plastic barriers, such as those available from E. I. Du Pont de Nemours and Co. (Wilmington, Del., United States of America), molded polyethylene or polypropylene, such as those available from Rexam (Evansville, Ind., United States of America), COVEXX from Wipak (Finland), multilayer plastic, metals, thermoplastics, thermoset plastics and combinations thereof.

When spacers are used, the spacing materials used in the sorbent bed may preferably be lightweight, rigid and include a fluid-impermeable perimeter. As the spacing materials are used to help define at least one of the refrigerant and fluid flow paths, and often both of such flow paths, the spacing materials are also preferably inert to both the refrigerant and coolant used in the sorption cooling system. Preferred spacer materials include polyethylenes, polycarbonates, polypropylenes, acrylonitrile-butadiene-styrene, polyoxymethylenes (e.g., DELRIN available from E. I. Du Pont de Nemours and Co.), polyvinyl chlorides, chlorinated polyvinyl chlorides, epoxies, thermoset polyester elastomers (e.g., HYTREL available from E. I. Du Pont de Nemours and Co.), polyphenylene ethers (e.g., NORYL available from General Electric Corp., Fairfield, Conn., United States of America), polyamides (e.g., NYLON available from E. I. Du Pont de Nemours and Co.), polyphenylene sulfides (e.g., RYTON available from Chevron Phillips Chemical Company, The Woodlands, Tex., United States of America), polytetrafluoroethylenes (e.g., TEFLON available from E. I. Du Pont de Nemours and Co.), polyvinylidine difluorides and combinations thereof. Of these, polyethylenes and polypropylenes may be particularly preferred spacer materials. In some instances, the desiccant sheet material may also be fabricated to the size of the desired spacer and utilized as the spacing material.

The desiccant sheets of the sorbent bed are preferably lightweight, thin, have a high adsorption capacity and are adapted to be regenerated at a relatively low temperature. One preferred desiccant sheet includes a low-cost, high-capacity desiccant material, such as composite desiccant comprising a porous-support material having a high pore volume, controlled pore size and an adsorbent dispersed onto the porous support material, such as those desiccants described in commonly-owned U.S. Pat. No. 6,559,096 to Smith et al., which is incorporated by reference herein in its entirety.

The high-capacity desiccant is preferably capable of adsorbing at least about 0.2 grams of liquid refrigerant per gram of desiccant, preferably at least about 0.5 grams of liquid refrigerant per gram of desiccant, more preferably at least about 1.0 grams of liquid refrigerant per gram of desiccant, and even more preferably at least about 2.0 grams of liquid refrigerant per gram of desiccant. The high-capacity desiccant also preferably has a relatively low ratio of heat of vaporization to heat of adsorption, such as less than 1:1.5, preferably less than 1:1.4, and more preferably less than 1:1.3. By way of comparison, a typical zeolite has a heat of vaporization to heat of adsorption ratio of about 1:1.8.

According to one embodiment, when the refrigerant consists essentially of water the preferred high-capacity desiccant can adsorb at least about 20 percent of its weight in water at 10 percent relative humidity at ambient temperature (e.g., 25° C.), and at least 40 percent of its weight in water at 50 percent relative humidity at ambient temperature. More preferably, the high-capacity desiccant will adsorb at least 40 percent of its weight at 10 percent humidity at ambient temperature and 60 percent of its weight at 50 percent relative humidity at ambient temperature. Even more preferably, the high-capacity desiccant will adsorb at least about 60 percent of its weight at 10 percent humidity at ambient temperature and at least about 80 percent of its weight at 50 percent humidity at ambient temperature.

Suitable desiccants include zeolites, barium oxide, magnesium perchlorate, calcium sulfate, calcium oxide, activated carbon, modified carbon, calcium chloride, glycerin, silica gel, alumina gel, calcium hydride, phosphoric anhydride, phosphoric acid, potassium hydroxide, sodium sulfate, and combinations thereof. A particularly preferred high-capacity desiccant is a surface modified porous support material. The porous support material can be a material such as activated carbon, carbon black or silica. A preferred support material is polytetra-floro-ethylene (PTFE). Preferably, the porous support material has a pore volume of at least about 0.8 cm³/g and average pore size of from about 1 nm to about 20 nm. The surface modification can include impregnating the porous support material with one or more metal salts, such as any one of calcium chloride, lithium chloride, lithium bromide, magnesium chloride, calcium nitrate, potassium fluoride and combinations thereof. The porous support material may be loaded with from about 20 to about 80 weight percent of the metal salt and such as from about 40 to about 60 weight percent of the metal salt.

The high-capacity desiccant is also preferably of such a nature and quantity as to desorb most sorbed liquid during the regeneration phase. In one embodiment, the high-capacity desiccant is capable of desorbing at least about 90% of adsorbed refrigerant at temperatures not greater than 120° C., preferably at least about 95% of sorbed refrigerant at temperatures not greater than 120° C. and more preferably at least about 98% of adsorbed refrigerant at temperatures not greater than 120° C.

The high capacity desiccant is useful for reasons other than its ability to regenerate at temperatures of not greater than 120° C. For example, the sorbent bed employed in the cooling system will generally be smaller than exhaust-type type cooling systems because of the high heat transfer coefficients of the liquid coolant as compared to the gas exhaust. The high sorption capacity of the desiccant enables a reduction in the necessary bed-volume due to its sorption performance. Parasitic (unrecoverable) losses may also be reduced. Moreover, when the regeneration of the desiccant is accomplished using low-grade waste heat, the only power required to operate the sorption cooling system is one or more electric fans and one or more coolant pumps, which yields a high effective COP, as discussed in further detail below. Improved fuel economy for vehicles and decreased emissions may also be achieved.

One particular desiccant sheet includes a porous PTFE sheet having a metal salt impregnated thereon. In a preferred embodiment, the desiccant sheets made of, inter alia, a PTFE sheet that is impregnated with a metal salt selected from the group consisting of lithium chloride and calcium chloride. Preferably the desiccant sheets include at least 0.01 grams of metal salt/cm² of sorbent side surface area, more preferably at least 0.02 grams of metal salt/cm², and more preferably at least 0.04 grams of metal salt/cm².

The desiccant sheets included in the sorbent bed may be in any suitable form so long as the desiccant sheets are in fluid communication with the refrigerant flow path and thermal communication with the coolant flow path. The cross-sectional area of the desiccant sheets may be (slightly) less than the corresponding cross-sectional area of the sorbent bed casing. As noted above, the cross-sectional area of the desiccant sheets may be increase to maximize the mass transfer and heat transfer capabilities of the sorbent bed.

The desiccant sheets generally have a relatively low thickness to enable efficient heat transfer between the coolant and the desiccant sheets. Preferably, the desiccant sheets have a thickness of not greater than about 5 mm, preferably not greater than about 2 mm, and more preferably not greater than about 1 mm. In one embodiment, the desiccant sheets comprise PTFE having a thickness of not greater than about 0.5 mm, such as not greater than about 0.25 mm, and at least about 0.05 mm.

The desiccant sheets should also be as light as possible to minimize the weight of the sorbent bed. The desiccant sheet should also be structurally sound to withstand forces from the refrigerant and fluid flows. The above-described PTFE sheets are particularly preferred due to their low weight and sturdy nature.

As noted above, a fluid impermeable layer should cover one side of the desiccant sheets to prevent unwanted interaction between the desiccant sheets and the fluid. The fluid impermeable layer should also be relatively thermally conductive to enable efficient heating and/or cooling rates between the fluid and the desiccant sheets. The fluid impermeable layer should also be lightweight to help minimize the weight of the sorbent bed. In this regard, fluid impermeable layer materials may include polyethylenes, polyurethanes, polyesters, COVEXX (available from Wipak, Finland) and metal foils. The fluid impermeable layer may be adhered to the desiccant sheet by any known method, such as lamination, ultrasonic welding, solvent welding and heat sealing.

Each of the desiccant sheets generally has at least one aperture. As noted above, the apertures define a portion of either the refrigerant or fluid paths. In one embodiment, the apertures define a portion of only the fluid flow path. In another embodiment, the apertures define a portion of only the refrigerant flow path. In yet another embodiment, a first set of apertures define a portion of the fluid flow path and a second set of apertures define a portion of the refrigerant flow path.

The desiccant sheets may have one aperture per sheet, but generally have a plurality of apertures per sheet. As the number of apertures increases, the number of fluid paths through the sorbent bed correspondingly increases and the total frictional surface area available to the fluid decreases. This correspondingly decreases the friction factor through the sorbent bed, which helps decrease the pressure drop through the sorbent bed. Moreover, when the apertures are a portion of the refrigerant flow path, increased numbers of refrigerant flow paths are created, which can lead to greater utilization of the desiccant material.

According to one embodiment, at least one of the desiccant sheets includes a plurality of apertures, such as at least 2, at least 4, at least 6, at least 8 and even at least 16 apertures per 40 in² (258 cm²) of cross-sectional area of each sheet. However, it will be appreciated that the number of apertures also increases the complexity of the plumbing that must be provided to fluidly isolate flow paths through the sorbent bed. According to one embodiment the desiccant sheets preferably contain not greater than 256 apertures, such as not greater than 128 apertures, and in some instances not greater than 64 apertures per 40 in² (258 cm²) of cross-sectional area of each sheet.

The desiccant sheets of the sorbent bed can have the same number of apertures per sheet or the desiccant sheets can have different number of apertures per sheet, depending on the desired fluid flow paths and pressure drop within the system. In one embodiment, a majority or even all of the desiccant sheets have the same number of apertures per sheet.

The orientation of the apertures through a desiccant sheet can be any orientation that enables efficient fluid flow through the device. In one embodiment, the apertures are substantially orthogonal to the sheet. The apertures in the desiccant sheets can be created by any known means, including laser cutting and die cutting.

The apertures can be any shape that enables efficient fluid flow through the sorbent bed. For example, the apertures can be substantially cylindrical, conical or a rectangular solid. In a preferred embodiment, the apertures are cylindrical to maximize the surface area available for sorption while maximizing the amount of fluid flow paths through the sorbent bed.

The apertures can be any width that enables efficient fluid flow through the bed while helping to maximize mass and heat transfer between the desiccant sheets with the refrigerant and fluid, respectively. The width/diameter of the apertures can be substantially the same or the size of the apertures can vary. In one embodiment, all the apertures have substantially the same width. In another embodiment, the width of the apertures is varied through the adsorbent bed to facilitate minimal pressure drop while helping to increase the number of fluid flow paths through the system. In one embodiment, the width of the apertures increases in a first direction across the plane of at least one of the desiccant sheets, such as across a majority or even all of the desiccant sheets.

In one embodiment, as depicted in FIG. 10, a first desiccant sheet 1412 and a second desiccant sheet 1412′ each include at least first, second and third apertures, 1401, 1401′, 1402, 1402′, 1403, and 1403′. The first apertures 1401, 1401′ have a first diameter, the second apertures 1402, 1402′ have a second diameter, and the third apertures 1403, 1403′ have a third diameter, where the first diameter is less than the second diameter, and the second diameter is less than the third diameter. The first apertures 1401, 1401′ are also aligned within a first flow plane 1401-FP of the sorbent bed. Correspondingly, the second apertures 1402, 1402′ and third apertures 1403, 1403′ are also aligned in a second and third flow plane, 1402-FP and 1403-FP respectively. These flow planes may be substantially parallel to one another. This arrangement provides multiple fluid flow paths through the sorbent bed while increasing fluid contact with the desiccant sheets with decreased pressure drop through the sorbent bed.

The desiccant sheets can be arranged in any suitable manner within the sorbent casing so long as efficient refrigerant and fluid flow paths are provided. In one embodiment, the desiccant sheets are substantially parallel to one another. In one embodiment, the apertures of a majority of the desiccant sheets are aligned within one another, as depicted in FIG. 10. In one embodiment, the substantially parallel sheets are substantially orthogonal to a refrigerant inlet, a refrigerant outlet or both. Correspondingly, the substantially parallel sheets may also be substantially parallel to a fluid inlet, a coolant outlet or both. In an alternative embodiment, the substantially parallel sheets are orthogonal to a fluid inlet, a coolant outlet, or both. Correspondingly, the substantially parallel sheets may also be substantially parallel to a refrigerant inlet, a refrigerant outlet or both.

The length and/or width of adjacent desiccant sheets may vary to help minimize flow imbalances within the system. In one embodiment, depicted in FIG. 11A, the width of the desiccant sheets 1512A decreases from the top of the bed to the bottom to help decrease flow imbalances of a fluid path (e.g., the coolant path) through the sorbent bed. As fluid enters the casing 1501A via the fluid inlets 1508A, in this instance from the bottom, the amount of force required for the fluid to enter the top of the sorbent bed will be more than the amount of force required for the fluid to enter the middle or lower portions of the sorbent bed as the fluid will want to follow the path of least resistance. However, as the motive force for flowing the fluid (e.g., a fan or pump—not depicted) is above the fluid outlet 1510A of the sorbent bed, the greatest motive force acting on the fluid will be at the top of the sorbent bed. Therefore, this tapered bed structure helps to balance the forces acting on the fluid at the various levels of the bed.

Another embodiment of a structure designed to help decrease flow imbalances is provided in FIG. 11B. Fluid flows through fluid inlets 1508B and exits via fluid outlet 1510B. Again, the motive force (not depicted) for flowing the fluid is disposed above the fluid outlet 1510B, thereby providing the greatest motive force at the top of the sorbent bed. However, in this embodiment the sorbent bed casing 1501B is tapered in relation to the sides of the desiccant sheets 1512B, and the desiccant sheets 1512B are all relatively the same size. As with the previous embodiment, this tapered bed structure helps to balance the forces acting at the various levels of the bed. It will be appreciated that while the foregoing tapered bed embodiments have been described in relation to a fluid, a refrigerant fluid could also be used in such embodiments. Additionally, both the desiccant sheet length/width and casing size could be varied to achieve the desired flow.

The space between the sorbent sides of the desiccant sheets has been found to be an important factor in sorbent bed performance, and relates to the mass transfer efficiency of and pressure drop of the refrigerant through the sorbent bed. Preferably, the space between the first adsorbent sides of two desiccant sheets (“the first gap size”) is such that the refrigerant contacts a large amount of desiccant with a small pressure drop. In one embodiment, the first gap size is not greater than 5 mm, preferably not greater than 2 mm, and more preferably not greater than 1 mm such as from about 0.5 mm to 1.0 mm. However, preferably the first gap size is at least 0.05 mm, preferably at least 0.1 mm, to decrease the amount of refrigerant pressure drop through the bed and help minimize complexity of manufacture. As noted above, the spaces between the desiccant sheets may be provided by the spacing materials, described above. Alternatively, the spacers may be eliminated and the gap may be provided by the pressure of the fluid.

With respect to the spaces between the second sides of the desiccant sheets (i.e., the fluid impermeable sides), these spaces relate to the volume of fluid and pressure required to flow fluid through the bed. Preferably, the space (“the second gap size”) between the second side of a desiccant sheet and a second material (e.g., another second side of a desiccant sheet or the fluid casing) is such that the fluid contacts a large amount of fluid impermeable layer surface area with a small fluid volume and small fluid pressure drop. In this regard, it will be appreciated that the volume of fluid is directly related to the second gap size and the phase of the coolant used (i.e., gas or liquid phase). For gaseous fluids, a greater volume of fluid will be required to achieve the same amount of cooling as compared to a liquid fluid. Therefore, liquids are generally preferred to cool and/or heat the sorption bed of the present invention. It will be appreciated that the type of fluid, surface area to be heated/cooled, fluid inlet and outlet temperature, regeneration temperature, cool-off temperature and thermal conductivity of the fluid impermeable barrier and desiccant material are all considerations in evaluating the appropriate second gap size.

The sorbent bed generally comprises a plurality of desiccant sheets. The number of desiccant sheets required is a function of several factors, including the desired cooling rate, which relates to the amount the evaporation rate of the evaporator, the type of refrigerant, the sorption capacity of the desiccant and the amount and size of sorbent beds utilized in the system. With this information a number of sheets can be calculated. For example, a cooling capacity of 7.2 kW-Hr is desired by many vehicle manufacturers. Assuming a sorption cooling system with one evaporator and three beds operating in the three operating phases (i.e., regeneration, adsorption and cool-off), that 3.2 grams per second of water is evaporated in the evaporator at steady-state (equivalent to 90% efficiency of the evaporator in translating water evaporation into cooled cabin air), that the high-capacity desiccant is adapted to adsorb 1 gram of water per gram of desiccant, and a cycle time of 5 minutes, then each sorbent bed must include 960 grams of high-capacity desiccant. Assuming that the desiccant sheets contain about 0.035 grams/cm² of desiccant material, about 27,450 cm² of desiccant sheet is required per bed (assuming thickness is negligible in relation to sorption capacity). If the area of the desiccant sheets cannot exceed 250 cm², 110 sheets would be required.

As noted above, the refrigerant flow paths of the sorbent bed provide fluid communication between the sorbent beds and the evaporator and condenser, depending on the respective operating phase of the beds. During regeneration operations the fluid communication includes the evaporation/desorption of the refrigerant from the desiccant into a carrier gas. During sorption operations, the fluid communication includes the sorption of the refrigerant onto the desiccant. Generally, the refrigerant flow paths should be defined to enable a high mass transfer rate within the bed at a low pressure drop. A high number of refrigerant flow paths should be utilized for greater sorbent utilization.

Preferably the pressure drop through the sorbent bed is as small as possible to reduce the size of the fans, pumps or other motive force required to circulate refrigerant and/or coolant therethrough. In one embodiment, the pressure drop of refrigerant flow through the sorbent bed is not greater than 4 inches of H₂O, preferably not greater than 2 inches of inches of H₂O, more preferably not greater than 1 inches of H₂O, and even more preferably not greater than 0.5 inches of H₂O.

The refrigerant flow paths are defined by the refrigerant inlet(s) and outlet(s) in the casing, and at least one of: (a) the apertures within the desiccant sheets, and (b) the spacing materials (if used). In one embodiment, a plurality of refrigerant flow paths are defined by a plurality of refrigerant inlets, outlets and apertures. Referring back to FIG. 9A, a plurality of refrigerant inlets 1004 are provided for the refrigerant to enter the adsorbent bed casing 1001. Spacing materials 1022 and apertures 1014 define the path through which the refrigerant fluid may flow. The fluid exits the bed through refrigerant outlets 1006.

The refrigerant flow path may be substantially linear or non-linear through the bed. A substantially linear flow path generally results in a low pressure drop, but may also result in an underutilization of sorbent. It may also be more difficult to plumb fluid to the desiccant sheets. One embodiment of an adsorbent bed having substantially linear refrigerant flow paths is illustrated in FIG. 12. Wet air flows through refrigerant inlet and into the sorbent bed casing. Various substantially linear flow paths provide fluid communication of the refrigerant to the desiccant sheets. Dry air exits the casing via refrigerant outlet. Coolant may be provided to the sheets to heat and/or cool such sheets.

As noted above, the refrigerant flow path may also be non-linear. A non-linear flow path generally has a higher pressure drop, but may result in an increased sorbent utilization. Ease of plumbing coolant may also berealized. One embodiment of an sorbent bed having multiple non-linear (i.e., tortuous) flow paths is provided in FIG. 9A, described above. Wet air flows through the refrigerant inlets 1004 and into the sorbent casing 1001. Apertures 1014 and spacing materials 1022 in the desiccant sheets 1012 help define non-linear flow paths for the refrigerant fluid to communicate with the first (adsorbent) side of the desiccant sheets. Dry air exits the casing via refrigerant outlets 1006. A fan (not shown) is generally used to circulate the air through the refrigerant flow paths.

The fluid flow paths are designed to provide high thermal exchange between the fluid and desiccant sheets with minimal volume, pressure drop and plumbing complexity. Like the refrigerant paths, the fluid paths are defined by the coolant inlet(s) and outlet(s), and at least one of: (a) the apertures within the desiccant sheets and (b) the spacing materials. Like the refrigerant flow paths, the fluid flow paths may also be linear or non-linear, and similar issues exist with respect to the fluid flow paths (e.g., pressure drop, heat transfer rate, plumbing complexity, etc.). The fluid flow paths are fluidly isolated from the refrigerant flow path to prevent interaction between the two streams. The fluid isolation is generally accomplished using the spacing materials and the fluid impermeable barrier on the second side of the desiccant sheet. The fluid flow paths are generally adjacent to the sorption sections of the desiccant sheet to thermally communicate therewith. The surface area of the fluid flow paths in contact with the desiccant sheets should be maximized for high heat transfer. The fluid is generally a liquid to enable high heat transfer, such as engine hot coolant from an internal combustion engine for regeneration operations, or cool coolant from a separate radiator for cooling operations.

The fluid flow paths can flow through the plurality of apertures or the spaces in the adsorbent bed, and the fluid generally flows through whichever path the refrigerant flow paths do not flow. Therefore, if the apertures are a portion of the refrigerant flow paths, the coolant flow paths would not be defined by the apertures and vice-versa.

Generally, the flow rate of fluid through the adsorbent beds is a function of the desired desiccant cooling/heating rate. Generally, temperature changes are exponentially related to difference in temperature between two objects. Therefore, flow rate in relation to temperature of the fluid and desired temperature and mass of desiccant to be cooled/heated must be evaluated to determine the appropriate coolant flow rate through the sorbent beds. In one embodiment, the mass of the desiccant sheets to cooling capacity ratio is <0.01 pounds per Watt-hour. During regeneration operations 1 kW of air drying may be achieved in five minutes with a desiccant sheet mass of less than 2 pounds.

The evaporator of the sorption cooling system may be any evaporative cooling type of evaporator adapted to cool a fluid stream in contact with at least a portion thereof. In one embodiment, the evaporator includes at least one thermally conductive sidewall for transferring thermal energy to the fluid stream proximal thereto, such as a wet-walled evaporator comprising a thermally conductive plastic wall. A useful evaporator is described in detail in U.S. Pat. No. 7,143,589 to Smith et al., which is incorporated herein by reference in its entirety.

In one embodiment, a single evaporator is used to provide cooling to incoming air. However, the size of such an evaporator may be too large for practical purposes. Thus, a multiple-stage sorption cooling system may be employed to achieve the desired cooling, where the multiple-stage sorption cooling system utilizes a series of evaporative coolers to cool the incoming cabin air. Using a multiple-stage sorption cooling system may enable a reduction in overall evaporator size due to efficiencies realized between the multiple sorbent beds, evaporators, and cabin air in contact therewith. See U.S. Pat. No. 7,143,589 to Smith et al.

One other potential benefit of the energy recovery multiple-stage system is that the size of the evaporators may decrease at each corresponding stage as less water will be required to be evaporated to achieve the desired cooling due to the lower temperature of the incoming air.

The effective COP of the vehicle sorption cooling systems described herein is relatively high. Generally, the only power required is that necessary to operate the coolant circulating pump, any necessary fans and any necessary valves. Thus according to one embodiment, the sorption cooling system has an effective COP of performance of at least about 8, preferably of at least about 10, more preferably of at least about 12 and even more preferably, of at least about 14. In this case, COP is defined as the realized cooling energy divided by the electrical power (i.e., the “wall-plug” efficiency).

The pressure within the evaporator, adsorber and refrigerant source of the sorption cooling systems may also be much less than generally required for a traditional compression-based air conditioner. Typically, the pressure within such components is preferably not greater than 14.7 psig (101.3 kPa), preferably not greater than 10 psig (68.9 kPa), more preferably not greater than 5 psig (34.5 kPa), and even more preferably not greater than 2.5 psig (17.2 kPa).

For automotive air conditioning (AC) and other applications for the generation of cooling via waste-heat utilization, engine coolant from the engine (for regeneration) and recirculated in a cooled, closed loop (sorption and bed cool-down after regeneration) may be used. For air/air systems, pressure drop and gas-side heat and mass transfer resistance are the major design issues.

For an air-air system, optimum channel lengths and gap spacing for the two different streams are on the same order. In contrast, for automotive AC, the ambient air is replaced with liquid which enables/requires a number of changes. Because of the high heat and mass transfer of liquids and the higher allowable operating pressures as compared to gases, channel length and gap size restrictions are greatly reduced and there is more freedom to optimize the design for the air side. Liquid manifolding between channels is much easier than for air flows because of reduced pressure drop concerns.

With liquid coolant, at least two new problems are encountered—complete sealing of the channels and pressure differences between the liquid and air streams causing deflection of the desiccant sheets. In fact, the pressure difference across the desiccant sheet will increase by 100-1,000 times as compared to an air-air system.

A heat and mass transfer model was developed for the liquid/air stack and used to model adsorption/heat transfer kinetics as a function of various design parameters for a nominal 1 kW bed. First, the required desiccant interface temperature for 1 kW which depends primarily on the gas phase mass transfer coefficient assuming that heat transfer is efficient enough to maintain the desiccant at a uniform temperature was calculated. This interface area was calculated to be 1.4 m² for 1 kW of cooling. The air gap was 0.5 mm and the air channel length was 30 mm. Since there are two desiccant sheets per air channel, the number of channels is fixed when the water flow length is fixed. Liquid pressure drop calculations led to selecting 300 mm as a nominal cooling/heating water flow length. This gave less than 5 psi pressure drop when using 0.5 mm water channel width. For the 1.4 m² of desiccant contact area, 100 parallel air and water channels are required. The first generation stack used this design. Subsequent generations used this same basic design except that the air channel length was shortened to 25 mm to reduce air-side pressure drop.

Desiccant optimization is typically thought to be critical to reduce adsorbent volume and mass. Because of the requirement for rapid and efficient heat and mass transfer, increases in desiccant bed size slow kinetics which requires further increases in bed size. However, the relatively high cooling requirement (e.g., 1.4 m² per kW of cooling) means that for the thickness range of desiccant sheet of 0.15 mm to 0.5 mm, there should be a large excess of desiccant capacity. “Standard” 50% impregnated LiCl and CaCl₂ desiccants, for which the typical 25° C. water isotherms are shown in FIG. 12A, have more than enough capacity. For 1 kW, water must be adsorbed at ˜0.4 g/seconds. Even with a 60 sec. cycle time, there is only 24 grams of water to adsorb per cycle. Therefore, standard CaCl₂ was utilized since it has greater stability under long-term repeated cycling and has reduced health and safety concerns.

A series of adsorbent stacks were fabricated for testing. Once a stack was produced, it was tested under a range of operating conditions. Initial tests will use dry air and measure flow rate versus pressure drop for the air side.

The test stand (FIG. 13) consists of a variable height Plexiglas channel in which dry air is flowing and a known amount of steam is injected. The fan provides the air and the flow rate is controlled by changing the fan speed. Air side pressure drop across the bed is measured with the differential pressure gauges.

The test stand is designed for a fixed length (300 mm) stack. During initial testing, it is found that the thermal response of the stack was limited by dead volume in the test stand and the use of four valves. Therefore, the system was modified with two special CPVC 3-way valves that were sequenced together by a computer control system. For the entire system, plastic construction is used as much as possible to minimize thermal mass and axial thermal conduction.

The stack design is such that the desiccant sheets can be easily changed if each channel has the same net heights. As the stack height decreases, the dead volume in each end of the stack decreases which also improved thermal cycling time.

Valve sequencing and data collection (temperatures, humidities, etc.) is accomplished with a computerized control system. This is important because of the rapid cycle times employed and the value of having all data collection on the same timescale.

The excellent thermal response of the stack and test system is shown in FIG. 14 for the stack design. For a range of inlet heating water flow rates, the change in the inlet temperature is essentially instantaneous and on the same order as the thermocouple response time. The inlet water temperature increases from ˜34° C. to 80° C. in ˜5 seconds. The outlet temperature has a slight lag related to the; 1) volumetric displacement in the stack and manifold, 2) small amounts of back-mixing from the manifold volume and 3) heat loss to flowing air (for the systems not marked “no air flow”). As expected, the faster the flow rate, the more rapid is the outlet temperature response. When no air is flowing, the response is not really more rapid but the outlet temperature rises to a higher value since the liquid is not being cooled by ambient air flowing at ˜30° C. In actual operation, the fan speed will be decreased from the high flow rate used during the adsorption part of the cycle to a slower flow rate to sweep water vapor out during the desorption step so the loss of thermal energy to air will be lower. For the 1 gpm test, the outlet temperature reached over 75° C. in less than 10 seconds. Note that because of the high heat transfer coefficients of the bed, the temperature within the sorbent bed will be above the water outlet temperature. The rapid heating of the bed and test stand clearly demonstrate how low the sorbent stack thermal mass is and points to very high thermal efficiency. Of course, these results do not include water desorption which will slow bed warm-up, but do show how rapidly the adsorbent beds can be cycled.

FIG. 14 illustrates the average bed temperature but does not illustrate anything about uniformity of heating. Excessive channeling could lead to fast “apparent” warm-up but would lower thermal efficiency and increase the required cycle time to achieve desorption. Therefore, infrared imaging is performed during a thermal cycle experiment using a flow rate of 1 gpm and at our final stack design. Because this is a surface modified stack through which ambient air has been flowing, this stack contains significant adsorbed water. Infrared imaging is taken on the exit side of the stack which means that the temperatures will lag slightly behind the actual temperature since the desiccant sheet does not penetrate to the outside surface of the stack. Infrared testing shows a stack with air flowing and 35° C. water flowing has a very uniform temperature. At time 0, the valves are switched and 83° C. water starts to flow into the stack. After only 8 seconds, the temperature is fairly uniform and on the order of 50° C. There are several channels that seem to be warmer indicating some minor flow non-uniformity. After 28 seconds, the average temperature is ˜60° C. and all locations are over 50° C. despite significant amounts of water desorption occurring. Finally, after 43 seconds, the average is over 70° C. and all locations are over 55° C. Again, since this is a surface temperature, it will be lower than the actual desiccants sheets.

The combination of inlet/outlet temperature cycling and infrared imaging clearly shows how quickly both the test system and the stack can be heated and cooled.

Four different adsorbent stacks are produced and tested. The differences between the stack include water and air channel gap size, the number of channels, the cross-sectional area, the manifold volume, and the mass of desiccant. All are similar in that they have plastic flow channels for the coolant/regenerating liquid that flowed in multiple parallel channels that were ˜300 mm long (see FIG. 15). The desiccant sheet could be replaced in each stack but only with a combination of two desiccant sheets and an air side flow spacer that has the same thickness. In other embodiments, the water gap and air gap thickness are fixed by the same, air side mesh spacer. Because of the differential pressure from the water to air side, the water channels are allowed to expand until the desiccant/flow mesh prevents further expansion.

Over the four adsorbent stack embodiment, various modifications are made to the stacks to: 1) reduce the manifold volume at each end, 2) reduce the amount of thermal mass arising from the spacers and desiccant, 3) improve sealing of the water channels/manifold, 4) reduce water side pressure drop and/or 5) improve flow uniformity. For stacks 3 and 4, the desiccant is switched from a carbon paper-based desiccant to a PTFE/carbon-based desiccant to obtain thinner sheets with higher desiccant loading. During testing, it is realized that the number of channels can be reduced from 100 to 50 and the fourth stack had only ½ the number of channels of the first three, which lead to another increase in performance because of the smaller dimensions. The key parameters for the four stacks are listed in Table 1. Key differences between stack 1 and 2 are in the water and air gap thickness and the approaches used to seal the stack.

TABLE 1 Key parameters of the four 1 kW adsorbent stack generations. Stack version #1 #2 #3 #4 Desiccant area (m²) 1.4 1.4 1.4 0.7 Desiccant type 0.5 mm 0.5 mm 0.15 mm 0.15 mm paper paper PTFE PTFE # of channels 100 100 100 50 Desiccant weight (g) 465 465 150 75 Total thermal mass 887 887 425 380 (g) Volume (liters) 2.0 2.0 1.4 0.8 These savings in the required desiccant amount and thermal mass may lead to a dramatic reduction in bed size over the four embodiments. For larger than 1 kW stacks, even better performance may be obtained on a kW basis because of the relatively fixed thermal mass of the manifolding.

FIG. 16 shows typical results for a test of the 4^(th) stack. In this experiment, the key measurements are the inlet and outlet water temperatures, the outlet air temperature, and the inlet and outlet vapor pressures in mbar. Vapor pressure instead of humidity is used since vapor pressure has direct meaning whereas humidity changes with temperature (i.e., 100% RH is a very different amount of water at 30° C. and 80° C.). For FIG. 16, a 60/50/10 cycle (adsorb for 60 seconds, desorb for 50 seconds and cool for 10 seconds) is used. There are 12 cycles where water vapor is fed to the bed followed by 7 cycles where the adsorption water is turned off. The water feed rate is 0.32 gram/second or a cooling load of ˜0.8 kW (note: 0.32 g/s×2,500 J/g ˜800 J/s or 0.8 kW). For this series of tests, the differences between the inlet and outlet water temperatures are barely distinguishable. When the cooling cycle and steam injection starts, the inlet vapor pressure quickly and repeatedly jumps to ˜45 mbar showing the advantage of using steam generation as a humidity source. How the steam generation is believed to work is that liquid water is flowed at a predetermined and well-controlled flow rate using a peristaltic pump into a heater which has sufficient power to vaporize the water. This superheated steam is then injected into the inlet plenum by the fan outlet when adsorbing and vented when desorbing/cooling. During desorption, the outlet air vapor pressure is running at ˜10 mbar so there is >80% capture efficiency despite having ½ of the desiccant contact area. The capture ratio may be further increased by increasing either the air flow length from the 25 mm fixed in the tests or by increasing the number of channels slightly. During desorption, the air outlet temperature rises from ˜35° C. to 55° C. However, this creates minimal thermal load since the air flow rate has been dramatically increased during this part of the cycle. The unexpected result is that after a few cycles to approach steady-state, the outlet water vapor pressure quickly rises to over a 100 mbar. This water vapor pressure rise could be further increased by optimizing the sweep air flow-rate.

The unanticipated implication of the results shown in FIG. 21 is that the adsorption cycle has the same time as the time for desorption and cooling cycles combined. This means that the number of beds can be advantageously decreased from the original 3 to only 2. In addition to immediately reducing bed volume and weight by ⅓, this greatly simplifies valving for both the liquid and air streams.

FIG. 17 shows an expanded picture of just one cycle for this same test. Note that the inlet vapor pressure takes ˜20 seconds to reach its final value at the start of an adsorption cycle. In testing, all streams are changed at once to start a cycle. However, if all sequencing is independent and optimized, one would start the “wet” air flowing to the stack before ending the desorption branch. In this fashion, even higher performance may be achieved by adjusting for the reproducible, system-dependent flow lag.

The elimination of one stack is very desirable but as long as the adsorption time is equal to the sum of desorption and cooling times, this is possible. Because this latest stack still has excess capacity (desiccant sheet is still not as thin as desired or possible), a longer cycle time is tested (120 s for adsorption, 110 s for desorption, 10 s for cooling). These results are shown in FIGS. 18 and 19. Because larger amounts of water are adsorbed, the desorption water vapor pressure is even higher (100-130 mbar) than the previous cycle. High desorption vapor pressure enables a smaller condenser and/or higher ambient air operating conditions since the condensation driving force is increased. Even after adsorbing for 120 s, the amount of water breakthrough (how much water vapor is leaving the bed) is low.

The testing reported above was at less than a 1 kW design water vapor injection rate (actually 0.8 kW) because of concerns related to running the steam generator near full output for extended time periods. In FIGS. 20 and 21, results are reported for a higher steam feed rate of 0.46 g/s (1.15 kW). For this test, a rapid cycle time of 30 seconds of adsorption, 20 seconds of desorption, and 10 seconds of cooling is used. Despite the higher water vapor feed rate and the fast cycle times, capture efficiency was above 75%. With higher water vapor feed rate, the air flow was also increased proportionally to maintain the same inlet water vapor pressure. Despite the rapid cycle times, outlet water vapor pressures in excess of 100 mbar is observed.

It was previously believed that the bed adsorption time would have to be 60 seconds for each step (180 seconds total cycle time) to have the bed mass/volume be practical. By reducing the thermal mass of the bed well beyond what was thought to be possible, cycle times three times faster than originally proposed can be achieved. With the current 0.15 mm desiccant, longer cycle times are possible. However, thinner desiccant sheets will both reduce the thermal mass further and enable operation at even shorter cycle times than the total cycle time of 60 seconds shown in FIGS. 20 and 21. Because of the reduced thermal mass and increased bed performance, multiple design options are available:

-   -   1) Keep the thicker 0.15 mm desiccant sheet run longer cycle         times. This would imply total desiccant weight of ˜3 pounds for         a 8 kW system but would have slightly higher energy efficiency         because of the reduced parasitic losses from rapid cycling; or     -   2) Use thinner desiccant sheets at 30-180 second total cycle         times. This would lead to another ˜50% reduction in desiccant         weight (which is already low compared to a vapor-compression         system).

The ability to run long cycle times relative to desorption/cooling cycles demonstrated with stack #4 above (i.e., reducing from three to two beds) raises the question of what would the performance be in a drying mode (i.e. simply removing water from ambient air). Drying is of great interest for improving the efficiency of auto AC, conventional AC when waste heat is available, and dehumidification. For cooling, it is desired to have the rate of water vapor flow to the condenser to be relatively constant so that the condenser and the recirculating stream may be optimized. For drying, the desorbed water does not need to be captured, so this is not an issue.

For this experiment, the water vapor feed rate was increased further to 0.5 g/s (1.25 kW) and ran long adsorption cycles as compared to the desorption/cooling cycles. FIGS. 22 and 23 show performance at the higher 1.25 kW cooling rate and a stack cycle time of 90/20/10 seconds. This means that the stack is sorbing 75% of the total time. Although the capture efficiency is lower (65-70%) at steady state because of the high duty cycle, this stack would be able to provide >1 kW of water removal with the current desiccant. If this stack was used in a drying mode, only a single adsorbent stack would be required. Sorption could occur for 70-85% of the time and quickly regenerate while desorbing water vapor to the atmosphere during the remaining 15-30%. This advantageously provides very simple plumbing for both the hot/cold liquid streams and the air stream to be dried.

While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, is to be expressly understood that such modifications and adaptations are within the spirit and scope of present invention. 

What is claimed is:
 1. An adsorbent bed, comprising: a fluid impermeable casing comprising a refrigerant inlet, a refrigerant outlet, a coolant inlet and a coolant outlet; a first desiccant sheet comprising a first aperture therethrough and a first adsorbent side; and a second desiccant sheet comprising a second aperture therethrough and a second adsorbent side; a refrigerant flow path for flowing a refrigerant fluid between said refrigerant inlet and refrigerant outlet, said refrigerant path being at least partially defined by said first and second adsorbent sides; and a coolant flow path for flowing a coolant fluid between said coolant inlet and said coolant outlet, said coolant flow path being fluidly isolated from said refrigerant flow path and being adjacent to at least one of said first and second desiccant sheets; wherein said first and second absorbent sheets comprise a hydrophobic polymer and a desiccant salt.
 2. An adsorbent bed as recited in claim 1, wherein the hydrophobic polymer is PTFE.
 3. An adsorbent bed as recited in claim 1, wherein the first and second desiccant sheets have a thickness of not greater than about 0.25 mm.
 4. An adsorbent bed as recited in claim 1, wherein the refrigerant flow path comprises mesh spacers.
 5. An adsorbent bed, comprising: a fluid impermeable casing comprising a refrigerant inlet, a refrigerant outlet, a coolant inlet and a coolant outlet; a first desiccant sheet comprising a first aperture therethrough and a first adsorbent side; and a second desiccant sheet comprising a second aperture therethrough and a second adsorbent side; a refrigerant flow path for flowing a refrigerant fluid between said refrigerant inlet and refrigerant outlet, said refrigerant path being at least partially defined by said first and second adsorbent sides; and a coolant flow path for flowing a coolant fluid between said coolant inlet and said coolant outlet, said coolant flow path being fluidly isolated from said refrigerant flow path and being adjacent to at least one of said first and second desiccant sheets; wherein the coolant flow path is formed by a pressure differential between the flowing refrigerant fluid and the flowing coolant fluid.
 6. An adsorbent bed as recited in claim 5, wherein the refrigerant flow path comprises mesh spacers.
 7. A closed-loop sorption cooling system, comprising: an evaporator; a condenser adapted for fluid communication with said evaporator; and at least first and second adsorbent beds adapted for fluid communication with said condenser and said evaporator, each adsorbent bed comprising: a fluid impermeable casing comprising a refrigerant inlet, a refrigerant outlet, a coolant inlet and a coolant outlet; a first desiccant sheet comprising a first aperture therethrough and a first adsorbent side; and a second desiccant sheet comprising a second aperture therethrough and a second adsorbent side; a refrigerant flow path for flowing a refrigerant fluid between said refrigerant inlet and refrigerant outlet, said refrigerant path being at least partially defined by said first and second adsorbent sides; and a coolant flow path for flowing a coolant fluid between said coolant inlet and said coolant outlet, said coolant flow path being fluidly isolated from said refrigerant flow path and being adjacent to at least one of said first and second desiccant sheets; wherein said first and second adsorbent beds have a cooling capacity of at least 1 kW per 350 grams of adsorbent (e.g., desiccant), such as at least 1 kW of cooling per 200 grams of adsorbent, and even at least 1 kW of cooling per 150 grams of adsorbent.
 8. The closed loop sorption cooling system of claim 7, wherein the system comprises no more than said first and second absorbent beds.
 9. A method for sorption cooling utilizing a an evaporator, a condenser adapted for fluid communication with said evaporator and at least first and second adsorbent beds adapted for fluid communication with said condenser and said evaporator, comprising the steps of: adsorbing a refrigerant in the first adsorbent bed; during said adsorbing step, desorbing a refrigerant from the second adsorbent bed; and during said adsorbing step and after said desorbing step, cooling the second adsorbent bed.
 10. A method as recited in claim 9, wherein said refrigerant comprises water.
 11. A method as recited in claim 9, wherein said desorbing step comprises heating the second absorbent bed using waste heat.
 12. A method as recited in claim 11, wherein the waste heat is derived from a vehicle engine.
 13. A method as recited in claim 11, wherein the waste heat is derived from a cogeneration facility. 